A candidate gene therapy vector delays vision loss in a mouse model of Bardet-Biedl Syndrome Type 10

Abstract

Purpose : The Bardet-Biedl Syndrome 10 (BBS10) protein, essential for the assembly of the BBSome, is critical for ciliary trafficking. Biallelic mutations in BBS10 are the second most common cause of BBS, leading to obesity, polydactyly, and vision loss. Subretinal gene therapy slowed vision loss in a BBS10 mouse model. Human-grade gene therapy vector candidates, AAV8-RK-hBBS10 and AAV8-CAG-hBBS10, were developed for clinical translation. In this study, we examine the hypothesis that the choice of promoter for driving BBS10 expression impacts therapy outcome in a murine model.

Methods : The human BBS10 gene driven by either the rhodopsin kinase (RK) promoter or the CMV enhancer/chicken β-actin promoter (CAG) was cloned into a shuttle plasmid, packaged into AAV2/8, and titered by quantitative PCR for in vivo gene delivery. For toxicity testing, 2.4×10¹¹ vg of either vector was subretinally injected into unaffected wild-type (WT) or heterozygous (HET) mice in a 2 µL volume, and optical coherence tomography (OCT) was performed at 1-, 3-, and 5-months post injection (MPI). For determining efficacy, Bbs10^-/- mice were subretinally injected with 2.4×10⁹, 2.4×10¹⁰, or 2.4×10¹¹ vg/eye of AAV8-RK-hBBS10, and outcome measures including electroretinography (ERG) and OCT were conducted at 1-, 2-, 3-, 5-, and 7-MPI. A visually-guided swim assay for rodent vision was conducted at 5- to 7-MPI.

Results : Unaffected HET or WT mice receiving 2.4×10¹¹ vg/eye of AAV8-CAG-hBBS10 showed thinning of the retina, whereas those that received AAV8-RK-hBBS10 did not. AAV8-RK-hBBS10 was designated the lead candidate vector. Following injections of AAV8-RK-hBBS10 at 2.4×10⁹, 2.4×10¹⁰, or 2.4×10¹¹ vg/eye, eyes of Bbs10^-/- mice that received the high dose had higher ERG amplitudes in the 5 Hz flicker test (20.7 ± 5.4 µV) compared to eyes that received the medium dose (10.9 ± 1.1 µV, p < 0.05), low dose (8.2 ± 2.1 µV, p < 0.005), and untreated eyes (6.5 ± 0.8 µV, p < 0.0001) at 2-MPI (averages ± SEM, two-way ANOVA, post-hoc Tukey’s test). Bbs10^-/- mice receiving the high dose took less time to find the platform compared to those that did not in a vision assay.

Conclusions : The choice of promoter impacts tolerability in vivo; AAV8-RK-hBBS10 had a superior tolerability profile. Mice with the BBS10 disorder treated with high dose AAV8-RK-hBBS10 had higher cone function and better functional vision compared to untreated mice.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.